Catalyst units are, among other tasks, used for cleaning of exhaust gases from combustion engines through oxidation of hydrocarbons and reduction of oxides of nitrogen. The units are commonly made as a ceramic carrier monolith body with parallel channels, and with a surface coating of catalytically active material such as platinum, palladium or other metals. The catalytic materials require an elevated temperature in use to reach full activity. If no special means are employed, the activity is lowest when the exhaust contains mostly hydrocarbons right after the start of the engine. There is always some low activity, and the increasing temperature of the exhaust due to the exothermic reaction at the oxidation of the hydrocarbons will heat the whole catalyst unit to an active temperature after a while.
Different ways to preheat the catalyst unit before starting the engine have been suggested, such as making the monolith of electrically conducting material which is then heated by electric current or by magnetically induced eddy currents. Another suggestion has been to blow hot clean gas through the unit. These suggestions have disadvantages in requiring expensive or bulky auxiliary equipment. The invention describes means for rapid heating of cathalyst units comprising ceramic carrier monolith bodies.